1. Field of the Invention
The present invention relates to an optical deflector that deflects and optically scans an incoming light, in particular, to an optical deflector that includes a movable base that is capable of being operated both at high speed and at large amplitude, and to an optical device that employs the optical deflector.
2. Description of Related Art
Conventionally, an optical deflector, which deflects and scans a beam of light, such as a laser light, is employed across a wide range of optical hardware, such as an electrophotographic copier, a laser beam printer, or a bar code reader. The optical deflector is also used in such hardware as a display device, which scans the laser light and projects an image thereby.
Such as a polygon mirror or a Galvano mirror are generally established as an optical deflector that performs an optical deflection in a mechanical fashion; refer to such as Japanese Patent Laid Open No. H07-175005, Japanese Patent Laid Open No. H06-180428, and Japanese Patent Laid Open No. 2003-121776. The Galvano mirror optical deflector is more amenable to miniaturization than the polygon mirror optical deflector. A prototype of a micro mirror, which employs a silicon substrate and which is manufactured using a micro machine technology, has been reported in particular as a miniature optical deflector.
The optical deflector that is disclosed according to Japanese Patent Laid Open No. H07-175005 is characterized by using electromagnetic power as to drive the optical deflector, and is configured so as to include a left-right symmetrical pair of permanent magnets that are positioned over or upon a base of the optical deflector, and a driving coil that is positioned in an external periphery of a reflecting mirror, wherein an electrical driving current is passed through the driving coil, alternating in a regular and a reverse manner. When the alternating regular and reverse electrical driving current is passed through the driving coil, the reflecting mirror unit is made to oscillate via a Lorentz Force that arises from an external magnetic field that is generated by the symmetrical pair of permanent magnets and the current that flows through the driving coil.
The optical deflector that uses the electromagnetic force experiences a decline in the Lorentz Force as an angle of deflection increases, and if an angle of rotation of the mirror is to be set to a large angle, it is consequently necessary either to increase the magnetic force of the permanent magnet, or else to increase the electrical current in the coil, with either approach incurring an increase in size and power consumption. Another problem is that a need to attach the permanent magnet prevents significantly reducing a size of an element.
The optical deflector that is disclosed according to Japanese Patent Laid Open No. H06-180428 is driven by using static electricity, with a driving electrode positioned directly beneath the reflecting mirror, in opposition thereto, with a minute gap therebetween, and a capacitor is configured from the mirror that is formed from a conductor, together with the driving electrode. The driving electrode is formed so as to be divided left and right, treating an axis of rotation of the mirror as an axis of symmetry thereof. When an electrical voltage is applied to an interval between the mirror and the driving electrode, the static electricity is generated, and the mirror is attracted toward the driving electrode, whereas applying the voltage alternately to the left hand and the right hand driving electrode causes the mirror to oscillate, revolving around the axis of rotation thereof.
While the optical deflector that uses the static electricity has an advantage in that it can be miniaturized because it can be manufactured solely using a semiconductor process, the static electricity is inversely proportional to the square of the distance between the mirror and the driving electrode, and thus, it is necessary to narrow the gap between the mirror and the driving electrode in order to apply sufficient static electricity to cause the mirror to oscillate.
Consequently, a rotational movement of the mirror is restricted by a contact between the mirror and the driving electrode, and thus, the angle of rotation of the mirror cannot be made large. Another problem is the format of driving by static electricity typically demands a high driving voltage of not less than 50 volts, which requires a dedicated driver IC.
The optical deflector that is disclosed according to Japanese Patent Laid Open No. 2003-121776 is driven by using static electricity, with a driving electrode positioned directly to a side of the reflecting mirror, in a comb-like fashion thereto, with a minute gap therebetween, and a capacitor is configured between the opposing comb-like driving electrodes. When an electrical voltage is applied to the interval between the opposing comb-like driving electrodes, the static electricity is generated, and the mirror is attracted toward the driving electrodes to either side thereof, and the force that causes the initial attraction, i.e., an initial inclination of the mirror, applies a force that causes the mirror to revolve around the axis of rotation thereof, and thus, causes the mirror to oscillate as a result.
While the optical deflector that uses the static electricity has an advantage in that it can be miniaturized because it can be manufactured solely using a semiconductor process, the static electricity ceases to have an effect as the angle of oscillation of the mirror increases and the teeth of the opposing comb come apart, and thus, it is not possible to make the angle of rotation of the mirror into a large angle.
Thus, the conventional optical deflector that uses electromagnetism or static electricity suffers from the problem of it not being possible to set the angle of rotation of the mirror to a large angle.
Accordingly, an optical deflector has been proposed that uses an oscillation of a piezoelectric actuator, as a technology that resolves such a problem as the foregoing; refer to Japanese Patent Laid Open No. H10-197819, Japanese Patent Laid Open No. 2001-272626, and Japanese Patent Laid Open No. 2003-29191.
The optical deflector that is disclosed according to Japanese Patent Laid Open No. H10-197819 comprises a plate shaped micro-mirror, a pair of rotation support bodies that support both sides of the micro-mirror, a framework unit that surrounds a periphery thereof, and a piezoelectric actuator that applies a translational motion to the framework unit.
The optical deflector that is disclosed according to Japanese Patent Laid Open No. 2001-272626 includes a support body, a voltage oscillator that is anchored to the support body and that moves in a reciprocating motion, a flexible body that is connected to the voltage oscillator, and a reflection plate that oscillates by being driven by the voltage oscillator, by way of the flexible body.
The optical deflector that is disclosed according to Japanese Patent Laid Open No. 2003-29191, with regard to a transformation mechanism thereof, links one end of each of a pair of columnar units via a hinge unit, interposes an actuator between the other end of each of the pair of columnar units, and positions a mirror, a flexible support unit, and a support substrate in a location upon or above the hinge unit.
What the preceding conventional technologies have in common is the fact that the piezoelectric actuator is conjoined to the mirror element substrate by way of the flexible body, and the oscillation of the piezoelectric actuator is thereby transformed into the rotational motion of the mirror. The optical deflector that uses the piezoelectric actuator is not restricted with regard to the rotation of the mirror, and thus, it is possible to obtain a large angle of deflection.
With regard to the preceding conventional technology, however, an optical deflector that comprises an assembly that transforms the translational motion of the piezoelectric actuator, by way of the flexible body, into the rotational motion of the mirror suffers from such problems as needing to conjoin, i.e., to attach, a plurality of configuration components to one another with a high degree of precision, such as the base plate, the piezoelectric actuator, the flexible body, and the mirror substrate, in order for the oscillation to be transmitted in an effective manner from the piezoelectric actuator to the mirror, and even if no problem is present with the conjoining of the plurality of components, it is possible that not all of the translational motion of the piezoelectric actuator may be transformed into the rotational motion, and thus, the mirror performs the translational motion as well as the rotation, which may result in a deviation in the beam light thereby.
The optical deflector according to the preceding conventional technology also suffers from the following problems from a process standpoint, in that it is difficult to miniaturize, owing to the fact that a bulk ceramic piezoelectric actuator and a flexible body that is formed from a metal plate or a rod is used as the configuration component therein, and furthermore, the fact that each respective configuration element is conjoined, i.e., assembled, using such as adhesives or solder means that it is not possible to assemble the configuration elements at a level of a silicon wafer, such as with a semiconductor device.
Thus, it is clear that the optical deflector that is implemented with the preceding conventional technology is neither significantly smaller, faster, or capable of achieving a significantly larger angle of displacement than the optical deflector that is implemented with the polygon mirror or the Galvano mirror, and, accordingly, an optical deflector has been desired that would be easy to manufacture using the semiconductor process technology, and, moreover, that would include both a high speed and a large angle of displacement.
Accordingly, an oscillating mirror has been proposed that is suited to being manufactured using the semiconductor process technology, as a technology that resolves the preceding problems; refer to Japanese Patent Laid Open No. 2005-128147.
The technology that is disclosed according to Japanese Patent Laid Open No. 2005-128147 involves forming an optical deflector of a piezoelectric unimorph oscillating body, a support body that includes a cavity unit that anchors and supports an end of a piezoelectric unimorph film that is formed directly upon or over the support body, a flexible body that is connected to the piezoelectric unimorph oscillating body and a reflecting plate that oscillates in a rotational manner within the cavity unit, in response to a driving impulse of the piezoelectric unimorph oscillating body, by way of the flexible body, wherein the piezoelectric unimorph oscillating body, the support body, the flexible body, and the reflecting plate are formed as a single structure.
Put another way, as depicted in FIG. 7, the technology that is disclosed according to Japanese Patent Laid Open No. 2005-128147 comprises a reflecting plate 01, a support body 09 that supports the reflecting plate 01, and a piezoelectric unimorph oscillating body 010, which causes the reflecting plate 01 to oscillate in a rotational manner. The piezoelectric unimorph oscillating body 010 comprises an oscillating plate 03a to 03d and a piezoelectric actuator 08a to 08d, which is formed from the voltage film that is formed directly upon or over the support body 09, wherein each respective oscillating plate 03a to 03d is connected to the support body 09 and the reflecting plate 01. The reflecting plate 01 is supported by the support body 09, by way of a flexible support unit 02a and 02b. 
The oscillating plate 03a to 03d, the support body 09, the flexible support unit 02a and 02b, and the reflecting plate 01 are formed of a single structure.
An operation of the preceding conventional optical deflector will be described hereinafter with reference to FIG. 8. FIG. 8 is a sectional cutaway view at a line between a point S10 to S10 in FIG. 7.
An alternating current, e.g., a sinusoidal current, is applied in phase to the piezoelectric actuator 08a and 08b, and to the piezoelectric actuator 08c and 08d in either an inverse phase or out of phase, thus causing the oscillating plate 03a and 03b, and the oscillating plate 03c and 03d, to oscillate. One end of each respective oscillating plate 03a and 03b, and one end of each respective oscillating plate 03a and 03b is anchored to and maintained in contact with the support body 09, and thus, while a lead drive unit 04a, 04b, 04c, and 04d oscillate in a vertical direction as denoted by an arrow R, the oscillation of the lead drive unit 04a and 04b is in a phase difference with the oscillation of the lead drive unit 04c and 04d. In particular, when the phase of the applied voltage is the inverse phase, the direction of the oscillation of the lead drive unit 04a and 04b is directly opposite to the oscillation of the lead drive unit 04c and 04d. 
Put another way, when the lead drive unit 04a and 04b move in the upward direction, the lead drive unit 04c and 04d move in the downward direction. In such a circumstance, a rotational torque, which is centered on the flexible support unit 02a and 02b, acts on the reflecting plate 01, causing the reflecting plate 01 to incline around a center axis of the flexible support unit 02a and 02b. A repeated vertical oscillation of each respective lead drive unit 04a and 04b and of each respective lead drive unit 04c and 04d, in response to the alternating current applied thereto, causes the rotational torque to act on the reflecting plate 01 in a see-saw manner, and thus, the reflecting plate 01 repeatedly oscillates in a rotational manner until it reaches a prescribed angle. The reflecting plate 01 oscillates in a rotational manner that is similar to the preceding, even when the lead drive unit 04a and 04b and the lead drive unit 04c and 04d are oscillating in the phase difference, rather than in the inverse phase.
When a driving frequency of the piezoelectric actuator 08a, 08b, 08c, and 08d is identical with or close to a mechanical resonance frequency of an assembly that brings together the reflecting plate 01 and the flexible support unit 02a and 02b, i.e., a movable mirror unit, the rotational oscillation of the reflecting plate 01 reaches its maximum, and a maximum angle of displacement may be obtained thereby, Setting the resonance frequency of the oscillating plate 03a, 03b, 03c, and 03d to be either identical with or close to the resonance frequency of the movable mirror unit makes it possible to obtain a large angle of rotation of the movable mirror unit. It is to be understood that it is possible to cause the reflecting plate 01 to oscillate in the rotational manner at the drive frequency of the piezoelectric actuator 08a, 08b, 08c, and 08d, even if the angle of rotation becomes small.
FIG. 9 shows an enlargement of a conjoining of the lead drive unit 04d and the reflecting plate 01, and, as depicted in the drawing, the oscillating plate 03d is conjoined to the reflecting plate 01 by way of the lead drive unit 04d. 
Whereas a width W01 of each respective lead drive unit 04a, 04b, 04c, and 04d, however, is set so as to be greater than a width W02 of the flexible support body 02a and 02b, and to be resistant to distortion, making each respective lead drive unit 04a, 04b, 04c, and 04d too large makes a mass of each respective lead drive unit 04a, 04b, 04c, and 04d excessively large, and causes the amplitude of each respective lead drive unit 04a, 04b, 04c, and 04d to become small. Hence, a limit exists to an extent to which a durability of each respective lead drive unit 04a, 04b, 04c, and 04d may be increased.
Consequently, when the oscillating plate 03a to 03d is oscillating in a circumstance, and the force that is generated thereby is transmitted to the reflecting plate 01, wherein each respective lead drive unit 04a, 04b, 04c, and 04d is actually oscillating, then an alteration occurs in each respective lead drive unit 04a, 04b, 04c, and 04d, such as is depicted in FIG. 10, and as a result, the force is not sufficiently transmitted to the reflecting plate 01, and the angle of oscillation cannot be made large.
Thus, it is clear that the optical deflector that is implemented with the preceding conventional technology is neither significantly smaller, faster, or capable of achieving a significantly larger angle of displacement than the optical deflector that is implemented with the polygon mirror or the Galvano mirror, and, accordingly, an optical deflector has been desired that would be easy to manufacture using the semiconductor process technology, and, moreover, that would include both a high speed and a large angle of displacement.